1. Field of the Invention
The present invention relates to a method of and an apparatus for controlling the pH and electric conductivity of water, and more particularly to a method of and an apparatus for controlling the pH and electric conductivity of water which are suitably used for suppressing corrosion of metals of such as a heat exchanger and piping of a cooling and heating system in which high-purity water is used as a heat transfer medium.
2. Description of the Related Art
Corrosion in high-purity water is influenced by the flow rate of water and dissolved oxygen, and is also affected by the pH of water. FIG. 1 shows the relationship between the pH and solubility of various copper ions at 25.degree. C. From this drawing, it can be seen that the corrosion of copper can be suppressed by using water of pH 9.
The pH control is generally performed by adding such chemicals as cyclohexylamine, morpholine, ammonia and caustic soda in addition to hydroquinone which is generally used in boiler water. This described in, for example, "Boshoku Gijutsu Binran" (Handbook of Corrosion Technology) complied by the Association of Corrosion Prevention (1986), pp. 643-644.
However, there have been drawbacks in that such chemicals, if added in excess, can accelerate corrosion. The electrical conductivity of water increases as the chemicals are added for replenishment to maintain the pH to an appropriate level, thereby promoting corrosion. Moreover, the electric conductivity of the water cannot be controlled by adding chemicals.